erst·while 
/ˈɚstˌwajəl/ adjective
always used before a noun /ˈɚstˌwajəl/ adjective formal : in the past : former
▪ erstwhile friends [=people who were friends in the past] ▪ erstwhile allies/enemies/lovers
▪ erstwhile friends [=people who were friends in the past] ▪ erstwhile allies/enemies/lovers
